This project will continue our investigations of human intestinal function and focus on the mechanisms of diarrhea. 1. Short-chain fatty acids (SCFA): a) Question of rate-limiting step common to absorption of acetate (C2), propionate (C3) and butyrate (C4) in human jejunum and ileum by perfusion of SCFA's singly and in combination. b) Effect of SCFA's on intestinal propulsion, evaluated by dye-dilution studies during "slow" marker perfusions. c) Colonic absorption capacity of SCFA in man studied by standard perfusion experiments. 2. Effect of colonic carbohydrate fermentation on stool weight and SCFA content. Graded doses of glucose infused into the cecum of normal subjects, with C14-PEG marker. Calculate increment of stool SCFA per gram glucose and minimal glucose dose effective in increasing stool weight. 3. Intestinal handling of lactose in lactase-deficient subjects: lactose meals during intestinal "slow" marker perfusion: is increase in flow rate entirely due to intact lactase or to bacterial fermentation? 4. Colonic interference with small intestinal transport: Colonic secretion will be induced by perfusion with 2-OH bile acid and with ricinoleic acid: will this affect fasting and postcibal flow rates in the small intestine? 5. SCFA absorption kinetics in the rat colon: everted mucosal sacs; including effects on SSC. 6. Effect of ricinoleic acid and prostaglandin E2 on rat colon in vitro: are effects similar to those of oxyphenasitin, deoxycholate and cholera enterotoxin? 7. Clinical studies on patients with the WDHA syndrome.